During laparoscopic surgery carbon dioxide gas is insufflated into the peritoneal cavity to create a working space between the interior abdominal wall and the abdominal organs. Other gases than carbon dioxide have also been used. An item of medical equipment known as an insufflator unit is used to regulate and control the delivery of gas between a gas supply, such as from a gas cylinder, and the patient.
Delivery of gas which is at high pressure in the gas cylinder to the low pressure environment of the patient necessitates gas expansion within the insufflator unit. The expansion of this gas results in considerable heat being lost from the gas and hence there is the potential for gas to be delivered to the patient at somewhat less than room or body temperature. Testing has shown that gas temperature can be as low as 14.degree. C. compared to the standard body temperature of 38.degree. C.
There has been some clinical experimentation performed to evaluate whether heating the gas used during laparoscopic surgery provides benefits to the patient. These benefits have been found to consist of less post-surgical pain and less lowering of core body temperature during longer procedures. Insufflation units have been proposed, therefore, which have the ability to deliver heated gas to the patient. This is seen as a significant improved feature over other units available. The delivery of heated gas is normally achieved not only by heating the gas within the insufflator unit but supplementing this heating by heating the gas in the line between the insufflator and the patient. One such device is known as a Cook Medical Technology LINS-1000 Insufflator which provides a disposable heated gas line apparatus to enable delivery of heated gas to a patient.
More recently, however, it has been proposed that humidification of the gas being supplied to a patient should also be carried out. Research has ascertained that once dry heated gas enters the peritoneal cavity, which is a moist environment, considerable body heat is used to humidify this heated but dry gas.
U.S. Pat. No. 5,411,474 discloses a humidification apparatus for insufflation gas for medical procedures. A temperature sensor is used to measure the temperature of the humidified gas at the outlet of the humidifier. By this means, there is an attempt to maintain a constant temperature of the humidified gas as it enters the patient but because the gas flow rate may vary there is no control of the degree of humidification. As gas flow rates may vary from one liter per minute to twenty five liters per minute, the humidity of the gas such as carbon dioxide may not be at an optimum or preferred level.
It is the object of this invention to provide a humidification arrangement for gas supplies to a patient whether the gas supply be for the purpose of laparoscopic surgery or other procedures which will overcome some of the above problems or at least provide the public with a useful alternative.